Control for hydrodynamic machines



April 29, 1941. R. E. DAVIS CONTROL FOR HYDRODYNAKIC MACHINES Filed Aug. 18, 1959 Control Vq/va 3 -TI l Patented pr. 29, 194i UNITED STATES PATET OFFICE 2,239,882 l CONTROL FOB, HYDRODYNAMIC MACHINES Richard E. Davis, Milwaukee, Wis., assignor to The Oilgear Company, Milwaukee, Wis., a corporation oi' Wisconsin Application August i8, 1939, Serial No. 290,742

(Ci. S-37) This invention relates to controls for hydrodynamic machines of the type which function as pumps when driven from a source of power and function as motors when supplied with motive liquid.

In certain types of machines which are driven by rotary hydrodynamic motors, it is desirable that the motor operate rst a1; one speed for a predetermined period of time and then operate at a different speed. In operating certain types -of hydraulically operated machines, it is advantageous to supply motive liquid thereto -iirst at ;one rate andthen at a higher rate and this is particularly true of machines of the type having two slides or carriages which are operated in sequence by hydraulic motors and the motor for operating the rst slide ls smaller than the motor for operating the second slide.

The present invention has as an object to provide a hydrodynamic machine with a control at one rate and then at another rate when iunctioning as a pump or to operate in either direc-V tion first at one speed and then at another speed Whenfunctioning as a'motor.

Other and more specific objects and advantages will appear from the description hereinafter given of a control in which the invention is embodied.

According to the invention in its general aspect and as ordinarily embodied in practice, a hydrodynamic machine iszprovided with means for rapidly increasing its displacement a predetermined amount, then maintaining the displacement nearly constant for a brief period of time and then rapidly increasing in displacement to a predetermined maximum.

According to the invention in another aspect, the displacement varying member of a hydrodynamic machine is rapidly shifted a predetermined distance in either direction from its neutral position, then moved very slowly for a brief period of time and then rapidly shifted to a predetermined limit.

Since the function of a pump and the function of a motor are substantially opposite to each other, the invention will be explained as applied to a hydrodynamic machine which is to function as .a pump but it is to beunderstood that the invention is equally applicable toa motor and that the term pump as used herein is intended to cover either a pump or a motor or a hydrodynamic machine which may function as either a pump or a motor.

The invention is exemplied by the apparatus shown somewhat schematically in the accompanying drawing in which the views are as follows: s

Fig. 1 is in part a transverse section through a pump to which the invention has been applied` and in part a diagram of the hydraulic circuit.'

the control mechanism being greatly enlarged relative to the -pump and the parts shown in the positions occupied when the displacement of the pump is zero.

Fig. 2 is an enlarged view of that part of the control mechanism in which the invention primarily resides, the valve being shown in the position occupied when the pump is delivering liquid at a predetermined maximum rate in one direction. y

Fig. 341s a view of a part of the mechanism shown inlFig. 2 buty shows the valve in a position intermediate the positions shown in Figs. l and 2. Fig. lis a view similar to Fig. 3 but with the valve shown in the position occupied when the pump 4is delivering liquid at a predetermined maximum ratein' the opposite direction.

Fig. 5 is a view similar to Fig. 3 but showing the valve in a position intermediate the positions shown in Figs. 1 and 4.

. For the purpose of illustration, the invention has been shown as being applied to a .pump I of the rolling pistontype but it is equally applicable to other types of pumps and motors. Since a pump of the rolling piston type is fully illustratedand described in ,Patent No. 2,074,068, the pump has not been shown in detail. It is deemed sunicient to state herein that pump I has its pistons and cylinders arranged radially in a "cylinder barrel 2 which rotates upon a stationary valve sha'fl; or pintle 3 having formed therein ports and passages through which liquid flows to and from the cylinders, that the outer ends of the pistons react against an annular reaction surface l which in practice is formed in a sepa-V ing upon the direction and the distance the axis of reaction surface 8 is odset from the axis of cylinder barrel 2, and that slide block i is arranged in a casing 6 which permits it to be moved transversely of pintle 3 but prevents it from moving in any other direction.

-distance slide block 5 is moved from its neutral position.

In order that pump I may be supplied with liquid to compensate for leakage losses and in order to compensate for the difference in the volume delivered by pump I and the volume returned thereto from an external circuit having differential motors connected therein, means are provided to permit liquid returned to pump I in excess of pump requirements to be discharged into a, reservoir 9 and, when the volume returned to the pump is less than pump requirements, to permit the pump to draw the required additional liquid from reservoir 9.

As shown, communication between pump I and reservoir 3 is controlled by an automatic valve I5 having'two spaced apart heads or pistons I8 and I1 arranged thereon and closely fitted in a bore I8 formed in a valve casing I9 which is arranged below slide block 5 and has a. part thereof extending into the liquid in reservoir 9.

Pistons I6 and I1 control communication between bore I8 and the lower ends of channels 1 and 8 which are connected to bore I8 at points spaced from opposite ends thereof. The extreme left end of bore I8 is connected by a channel 28 to channel 1 intermediate the ends thereof and the extreme right end of bore I8 is connected by a channel 2I to channel 8 intermediate the ends thereof.

That part of bore I8 between channels 1 and 8 communicates with a chamber 22 formed in the lower part of valve casing I9 and communieating with reservoir 9 through a check valve 23 which permits pump I to draw liquid freely from reservoir 9 but prevents' liquid from being expelled from "chamber 22 except through a low pressure relief valve 24 having its inlet connected to chamber v22.

'I'he arrangement is such that, when pump I,

starts to deliver liquid into channel 8, pressure extends from channel 8 through channel 2I to the right end of bore I8 and shifts valve I5 toward the left so that channel 8 is blocked by piston I1 and channel 1 is opened to chamber 22 through bore I8 and, when pump I starts to deliver liquid into channel 1, pressure extends from channel 1 through channel 20 to the left end of bore I8 and shifts valve I5 toward the right to the position shown so that channel 1 is blocked by piston I8 and channel 8 is opend to chamber 22 through bore I8.

aasaeea Pump I is caused to deliver liquid in one direc-A tion or the other by shifting slide block 5 in one direction or the other from a central or neutral position. This is accomplished by hydraulically actuated means operated by liquid supplied thereto by a gear pump 21 which draws liquid from reservoir 9 and discharges it into a low pressurel supply channel 28, the liquid discharged by gear pump 21 in excess of requirements being exhausted through a low pressure relief valve 28 which discharges into reservoir 9 and enables gear pump 21 to maintain a. uniform pressure in channel 28.

Slide block 5 is adapted to be moved toward the left by a compound servo-motor consisting of a cylinder 30 which is xed to pump casing 6 and provided at its outer end with an end head 3I, a piston 32 which is fitted in cylinder 30 and abuts or is connected to slide block 5, and a piston 33 which is fitted in cylinder 30 between piston 32 and end head 3I. The outer end of cylinder 30 is sealed by a cap 34 which is fixed to head 3 and has an adjusting screw 35 threaded therethrough to limit the movement of slide block 5 toward the right.

Adjusting screw 35 coacts with a stop rod 36 which extends loosely through head 3I and pistons 32 and 33 so that its left end may be engaged by slideblock 5. Stop rod 36 has a nut 31 threaded thereon and arranged in a suitable recess formed in head 3l, and it has a collar 38 xed thereon and arranged in a suitable recess formed within piston 33.

Liquid for operating servo-motor 38-33 is supplied thereto by gear pump 21 under the control of a valve 39 which has a branch of supply channel 28 connected thereto and is adapted to permit liquid toy escape from cylinder 38 into a drain channel 40 which discharges into reservoir 9. Control valve 39 has one of its ports connected by a channel 4I to cylinder 30 at or near the outer end thereof and another of its ports connected by a channel 42 to cylinder 30 at a point between pistons 32 and 33.

The arrangement is such that, when control valve 39 is shifted to one of its three positions, it connects channels 4I and 42 to drain channel 48 and permits mechanism to be presently described to shift slide block 5 toward the right ward the right until it engages adjustinglscrew' 35 which arrests further movement of slide block 5 and thereby limits the displacement of pump I and the rate at which liquid is delivered into channel 1.

When control valve 39 is shifted to its neutral position, it connects channel 4Iv to supply channel 28 and connectschannel 42 to drain channel 40 so that liquid from gear pump 21 may flow through channel 28, valvev 39 and channel 4I to the outer en'd of cylinder-*30 and cause piston 33 to move slide block 5 toward the left. Piston 33 will engage collar 38 and move stop rod 36 toward the left until further movement thereof is arrested by nut 31 which is adjsted to stop rod 36 and piston 33 when slide block 5 reaches its central or neutral position at which time pump I ceases to deliver liquid.

When control Vvalve 39 is shifted to its third position. it connects both of channels 4I and 42 to supply channel 28 so that both faces of piston any deficiency in the liquid returned to the pump 33 are'subjected to gear pump pressure and liquid may flow'through chaannel 42 and cause piston 32` to shift slide block `5 toward the left until further movement thereof is arrested by a stop to be presently described. Shifting slide block toward the left from its neutral position causes pump l to deliver liquid into channel 8.

The mechanism for moving slide block 5 toward the right is best shown in Fig. 2. As shown, slide-block 5 is continuously urged toward the right by gear pump liquid acting upon a piston 45 which abuts or is connected to slide block 5 and fitted in a cylinder 46 carried by pump casing 6. Cylinder 46 is closed at its outer end by a valve block 41 which has a central bore 48 formed therein and closed at its outer end by a cap 49 having an adjusting screw 58 arranged therein.

Bore 48 has tted therein a valve ,5| which is y attached to piston 45 to move therewith and formed in the wall thereof between two ports 55 and 56 which are formed in valve block 41 and extend around bore 48 so as to leave two very narrow lands 51 and 58 upon opposite sides of port 54. Piston 55 coacts with lands 51 and 58 to momentarily stop the ilow of liquid through bore 54 and thereby momentarily arrest the movement of slide block 5 in one direction or the other from its neutral position as will presently ap'- pear.

Port 55 has a branch of channel 28 connected thereto. Port 56 communicates with cylinder 45 and is connected to port 55 through a passage 59 having an adjustable throttle valve 65 arranged therein to limit the rate of liquid now therethrough. The arrangement is such that pressure created by gear pump 21 extends through channel 28, port 55, bore 48 and port 56 to cylinder 46 and causes piston 45 to continuously urge slide block 5 toward the right. However, piston 45 is considerably smaller than pistons 52 and 33 so that it cannot move slide block 5 toward the right until cylinder is opened to drain, and lservo-motor 52-33 when energized may readily move slide block 5 toward the left against the resistance of piston 45.

In order that slide' block 5 may be returned rapidly to its neutral position, port 54 is connected by a channel 5l to the inlets of two check valves 62 and 55 the outlets of which are connected, respectively, by channels 64 and 55 to ports 55 and 54. If it is desired that the movement of slide block 5 toward its neutral position be momentarily arrested, channels 6l, 54 and 65 and check valves 52 and 63 are omitted.

, Operation "Assuming that pumps i and 2li are running and that valve 35 is in its neutral position so that slide block 5 ls in its neutral position, the control will function as follows:

When valve 39 is shifted to a position to con- 46 through port 56, bore 48 and port 55 into channel 28 until valve piston 53 blocks the flow ofliquid through bore 48 by moving into alignment with land 51 as shown in Fig. 3.

The liquid expelled from cylinder 46 must then flow through passage 55 at a very low rate as determined by the adjustment of throttle valve 60 so that slide block 5 must move very slowly until valve piston 53 moves out of alignment with land 51 and permits liquid to again now freely through bore 48 as shown in Fig. 2. Then slide block 5 will move at a very high speed until valve 5l engages adjusting screw 50 which is adjusted l to stop slide block 5 when the rate at which pump i is discharging liquid into channel 4 reaches a predetermined maximum.

When slide block 5 is at the limit of its movement toward the left as indicated by the position of valve 5l in Fig. 2 and control valve 59 is rey slide block 5 is moved at high speed until stopped in its neutral position by piston 33.

When slide block 5 is in its neutralposition and control valve 39 is shifted to a position to connect channels 4l and 42 to drain channel 45, liquid from gear. pump 21 will flow through channel 28, port 55, bore 48 and port 56 to cylinder 46 and cause piston 45 to move slide block 5 and valve 5l toward the right at a very high speed until valve piston 53 aligns with land 58 as shown in Fig. 5 and then the liquid will flow through passage 55 at a very low rate as determined by the adjustment of throttle valve 55 and cause piston 45 to move slide block 5 toward the rightl at a very slow speed as long as piston 55 remains in alignment with land 55. As soon as piston 53 moves beyond land 54 as shown in Fig. 4, liquid may flow freely through'bore 48 and cause piston 45 to again move slide block 5 toward the right at a very high speed until it moves stop rod 55 against adjusting screw 55 which is adjusted to stop slide block 5 when the rate at which pump i is discharging liquid into channel l reaches a predetermined maximum. l

When slide block 5 is at the limit of its movement toward the right as indicated by the position of valve 5l in Fig. 4 and control valve 55 isreturned toits neutral position so that channel 4i is opened to gear pump pressure, liquid from gear pump 21 will ilow therethrough to cylinder 35 and cause piston 55 to shift slide block 5 toward the left and piston 45 to expel liquid from cylinder 45. Slide block 5 will moveV at a very high rate of speed and liquid will now freely from cylinder 45 through port 55, bore 45 and port 55 into channel 23 until valve piston 55 blocks the now of liquid through bore 45 by moving into alignment with land 55 as shown in Fig. 5 and then the liquid will bypass around piston 5l from port 55 through channel 65, check valve 53 and channel 6l to port 54 in bore 45 so thati slide block 5 is moved at high speed until piston 35 is stopped by collar 8B on rod 36 at which time slide block g 5 is in its neutral position and further movement thereof toward the left is prevented due to piston 45 being continuously subjected to gear pump pressure.

lThe arrangement is such that movement of valve et from its neutral position to one ci its other two positions causes slide bloei; to be suddenly shifted a predetermined distance in one direction or the other, then delayed for a brieiJ period of time and then suddenly shifted to a predetermined limit so that pump l is caused to deliver liquid at a predetermined rate, that rate maintained nearly constant for a brief period of time and then suddenly increased to a predetermined maximum.

The control thus enablesV a motor to operate at a given speed for a siven period of time and then antematlcally increase its speed to a predetermined maidmum, and it enables a pump to either drive a motor at 'a given speed for a given penod of time and then automatically accelerate the motor to a predetermined maximum speed or to drive one motor at a desired speed and then drive a second motor at a desired speed.

For example, the work slide and the tool slide o a certain type of breaching machine are operated in sequence by a small motor and a large motor. The invention enables a pump to at rst deliver liquid at a rate suitable for driving the work slide motor, to maintain that rate until the l work slide completes its stroke, and to then inv crease its delivery to a rate suitable for driving the tool slide motor.

The control is adapted for various other uses and it may be modied in various ways without departing from the scope of the invention which is hereby claimed as follows.

I claim:

l. In a hydrodynamic machine having a displacement varying member shiftable between zero and maximum displacement positions, the combination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, means effective only at a point between said positions for interrupting the rapid movement of said member, and means for modifying the effect of said interrupting means to enable said moving means to move said member at slow speed past said point whereby the displacement of said machine is suddenly increased a predetermined vamount and lthen maintained nearly constant for a predetermined period of time and then suddenly increased to apredetermined maximum.

2. In a hydrodynamic machine having a displacement varying member shiftable between zero and. maximum displacement positions, the combination of means for moving said member from its zero displacement position -to a maximum displacement position and tending to move it at high speed, means effective only at a point between said positions for interrupting the rapid movement of said member, means for modifying the effect of said interrupting means to enable said moving means to move said member at slow speed past said point whereby the displacement oi' said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a. predetermined maximum. means for moving said member` to its zero displacement position. and means for preventing said interruptlng means from interrupting the movement of said` member toward its zero displacement position.

3. In a hydrodynamic machine having a displacement varying member shif-table between zero and maximum displacement positions, the combiof means or moving said member from @incassa its aero displacement position to a maximum dis. placement position and tendina to move it at high speed, means eective only at a point between. said positions ier interrupting the rapid movement oi said member, means for modifying the edect oi said interrupting means to enable said moving means to move said member at slow speed past said point whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined mammum, and means for varying the speed of said member past said point to thereby vary the period of 'time during which the displacent of said machine is maintained nearly constant.

4. In a namic machine having a displacement v a -,.-:g. member shitable between aero and maximum displacement positions, the combination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, means edective only at a point between said positions for interrupting the rapid movement of said member, means for modifying the effect of said interrupting means to enable said moving means to move said'member at slow speed past said point whereby 4the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant ior a predetermined period of time and then suddenly ncreased to a predetermined mum, means for varying the s of said member past said point to thereby vary the period of time during which the displacement of said machine is malntained nearly constant, means for moving said member to its zero displacement position, and means for preventing said interrupting means from interrupting the movement of said member towarclits zero displacement position.

^ 5. In a hydrodynamic machine having a displacement varying member shiftable between zero and maximum displacement positions, the combination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, hydraulic means for resisting the movement of said member toward its maximum displacement position, means including a channel for supplying liquid to said hydraulic means, a valve movable with said member for controlling said channel and adaptedto close the same and interrupt the discharge of liquid therethrough from said hydraulic means when said member reaches a given point between said positions, and means for bypassing liquid around said valve at a limited rate to enable said moving means to move said member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement or said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum.

' 6. In a hydrodynamic machine having a. displacement varying member shiftable between zero and maximum displacement positions, the combination of means vfor moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, hydraulic means for resisting the movement o: said member toward its maximum displacement position. means including a channel for supplying liquid to said hydraulic means. a valve movable with said member for controlling said channel and adapted to close the same and interrupt the discharge of liquid therethrough from said hydraulic means when said member reaches a vgiven point between said positions, means for bypassing liquid around said valve at a limited rate to enable said moving means to movesaid member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of'time and then suddenly-increased to a predetermined maximum, and means for to said cylinder at a uniform pressure, a valve movable with said member Afor controlling said channel and adapted to close the same and interrupt the discharge of liquid therethrough from said hydraulic means when said member reaches a given point between said positions, means for bypassing liquid around said valveat a limited rate to enable said moving means to move said member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum, said piston being adapted to move said member to its zero'displacement position in response to said moving means being deenergized, and means for bypassing liquid freely around said valve during movement of said `member toward its zero displacement position.

8. In a hydrodynamic machine having a dis-'- placement varying member shiftable between zero and maximum displacement positions, the combination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high Speed, a stationary cylinder, a piston iitted in said cylinder and movable with said member, means including a channel for supplying liquid to said cylinder at a uniform pressure, a valve movable with said member for controlling said channel and adapted to close the same and interrupt the discharge of liquid therethrough from said hydraulic means when said member reaches a given point between said positions, means for bypassing liquid around said valve at a limited rate to enable said moving means to move said member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined-maximum, said piston being adapted to move said member -to its zero displacement position in response tosaid moving means being deenergized, means for bypassing liquid freely around said valve during movement response to said moving means being deenergized,A

of said member toward its zero displacement po` sition, and means for varying the rate at which liquid is bypassed around said valve to thereby vary the period of time during which the displacement of said machine is maintained nearly constant.

9. In a hydrodynamic machine having a displacement varying member shiftable between zero and maximum displacement positions, the combination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, a stationary cylinder, means including a channel for supplying liquid to said cylinder at a uniform pressure, a piston tted in said cylinder and adapted to move with said member and eject liquid from 'said cylinder through said channel, a valve plunger arranged in said' chanl nel and movable with said member, an annular valve seat formed upon the wall of said channel, an annular valve arranged upon said plunger to coact withV said valve seat and close said channel when said member reaches a given point between said positions, and means for bypassing liquid around said valve at a limited rate to enable said moving means to move said member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum. v

10. In a hydrodynamic machine having a displacement varying member shiftable between zero and maximum displacement positions, the cornbination of means for moving said member from its zero displacement position to a maximum displacement position and tending to move it at high speed, a stationary cylinder, means including a channel for supplying liquid to said cylinder at a uniform pressure, a piston iitted in saidcylinder and adapted to move with said member and eject liquid from said cylinder through said channel, a valve plunger arranged in said channel and movable with said member, an annular valve seat formed upon the wall of said channel, an annular valve arranged upon said plunger, to coact with said valve seat and close said channel when said member reaches a given point between said positions, means for bypassing liquid around said valve at a limited rate to enable said moving means to move said member at slow speed past said point and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined .maximum said piston being adapted to move said member to its zero displacement position in and means for bypassing liquid freely around said valve during movement of said member toward itsl zero displacement position.

11. In a` hydrodynamic machine having a displacement varying member shiftable in opposite directions from a zero displacement-position to one or the other of two maximum displacement positions, the combination of means for moving i `one or the other of said directions, and means l only one or the other oi two points for for modifying the effect o said interrupting means to enable said moving means to move said member at slow speed past either of said points whereby the displacement oi said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period oi time and then suddenly increased to a predetermined mammum during movement o said member in either direction.

i2. In a hydrodynamic machine having a' displacement varying member shiitable in opposite directions from a zero displacement positlon'ito one or the other of two maximum 1 positions, the combination oi means for moving said member in each of said directions and tending to move it at high speed, meansebective at interrupting the rapid movement ci said member in one or the other of said directions, means for modifying the effect of said interrupting means to enable said moving means to move said mein- 'ber at slow speed past either oi said points Wherem by the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum during movement of said member in either direction, and means for preventing said interrupting means from interrupting the movement of said member from a maximum displacement position to its zero displacement position.

13. In a hydrodynamic machine placement varying member shiftable in opposite directions from a zero displacement position to one or the other of two maximum displacement positions, the combination of means for moving said member in each of said directions and tending tomove it at high speed, means edective at only one or the other of two points for interrupting the rapid movement of said member in one or the other of said directions, means for modifying the eiect of said interrupting means to enable said moving means to move said member at slow speed past either of said points whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to apredetermined maximum during movement of 50 said member in either direction, and means for varying the speed of said member past either of said points to thereby vary the period of time during which the displacement of said machine is maintained nearly constant. 4

14. In a hydrodynamic machine having `a displacementvarying member shiftable in opposite directions from a zero displacement position to one or the other of two maximum displacementpositions, the combination of means for moving said member in each of said directions and tending to move it at high speed, means eiective at only one or the other oi two points for 'interrupting the rapid movement of said member inA one or the other of said directions, means for modifying the eilect of said interrupting means to enable said moving means to move said member at slow speed past either of said points whereby the displacement of said machine is suddenly increased a predetermined amount and 'then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum during movement of said member in either direction, means for varying the speed of said member past lacement" having a disasse,

points to thereby vary the period of time during which the displacement of said machine is maintained nearly constant, and means for prevent- .f

ing said interrupting means from interrupting the movent oi said member from a maximum displacement position to its zero displacement position.

l5. in a hydrodynamic machine having a disffwe vag member shiftable in opposite directions irom a aero displacement position to one or the other oi two maximum displacement positions, the combination of means for moving .s member in one direction and tending to move it at high speed, means for energizing and vita-autr said moving means, a stationary cylinder, a piston ntted in said cylinder and movable with said member, means including a chel for suppl liquid to said cylinder at a uniform pressure to cause said piston to expel liquid from said cylinder through said channel whm said member is moved in said direction by said moving means and to enable said piston to move said member in the opposite direction at high speed when said moving means is deenergized, valve means movable with said memmr and so positioned within said channel as to close it and thereby interrupt the rapid movement oi said member when said member reaches a predetermined point on one side or the other of its zero displacement position, and means for bypassing liquid around said valve means at a limited rate to enable said moving means or said piston to move said member at slow speed past one or the other of said points and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constantior a predetermined period of time and then suddenly increased to a predetermined maximum.

ld. vlin a hydrodynamic machine having a dis placement varying member shiftable in opposite directions from a zero displacement position to one or the other of two maximum displacement positions, the combination of means formoving by said moving means and to enable said piston to move said member in the opposite direction at high speed when said moving means is deenergized. valve means movable with said member and so vpositioned within said channel as to close it and thereby interrupt the rapid movement of said member when said member reaches a predetermined point on one side or the other or its zero displacement position, means for bypassing liquid around said valve means at a limited rate to enable said moving means or said piston to move said member at slow speed past one or the other of said points and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum, and means for bypassing liquid either of said freely around said valve during movement of said member from eitherof its maximum displacement positions to its zero displacement position.

17. In a hydrodynamic machine having a displacement varying member shiftable in opposite directions from a zero displacement position to one or the other of two maximum displacement positions, the combination of means for moving said member in one direction and tending to move it at high speed, means for energizing and deenergizing said moving means, aA stationary dylinder, a piston fitted in said cylinder and movable with said member, means including ,a channel for supplying liquid to said cylinder at a uniform pressure to cause said piston to expel liquid from said Vcylinder through said channel when said member is moved in said direction by said moving means and to enable said piston to move said meinberlin the opposite direction at high speed when said moving means is deenergized, valve means movable with said member and so positioned within said channel as to close it and thereby interrupt the rapid movement of said member when said member reaches a predetermined point on one side or the other of its Zero displacement position, means for bypassing liquid around said valve means at a limited rate to enable said moving means or said piston to "move said member at slow speed past one or the other of said points and thereby cause said valve to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum, and means for varying the speed of4 said member past either of said points to thereby vary the period of time during which the displacement of said machine is maintained nearly constant. y

18. In a hydrodynamic machine having a dischannel for supplying liquid to said cylinder at.

a uniform pressure to cause said piston to expel y liquid from said cylinder through said channel when said member is moved in said direction by said moving meansand to enable said piston to move said member in the opposite direction athigh speed when said moving means is deenergized, valve means movable with said member and so positioned within said channel as to close it and thereby interrupt the rapid movement of Asaid member when said member reaches a predetermined point on one side or the other of its zero displacement position, means for bypassing liquid around said valve means at a limited rate to enable said moving means or said piston to move said member at slow speed past one or the other of said points and thereby cause said valve e to open said channel whereby the displacement of said machine is suddenly increased a predetermined amount and then maintained nearly constant for a predetermined period of time and then suddenly increased to a predetermined maximum, means for varying the speed of said member past either of said points to thereby vary the period of time during which the displacement of said machine is maintained nearly constant, and means for bypassing liquid freely around said valve during movement of saidmember from either of its maximum displacement positions to its zero displacement position.

RICHARD E. DAVIS. 

